The cancer stem cell model proposes that a rare subpopulation of cells within a tumor possesses cardinal features of stem cells, namely self-renewal and multipotency, and that these cancer stem cells arise from oncogenic transformation of normal stem cells or related progenitors. Mouse models of prostate carcinoma represent an excellent system in which to explore the implications of this model, and to identify putative cell types of origin for cancer as well as tumor-initiating cells. In previous studies, we have used genetic lineage-tracing in vivo to identify a rare luminal stem cell population marked by expression of the Nkx3.1 homeobox gene (termed CARNs). We have shown that deletion of the Pten tumor suppressor together with activation of Kras in CARNs results in prostate carcinoma, indicating that this cell population is an efficient cell of origin for prostate cancer. Transplantation of CARNs that have undergone deletion of Pten and activation of Kras results in the formation of renal grafts with PIN and carcinoma phenotypes, suggesting that transformed CARNs correspond to tumor-initiating cells. Furthermore, we have identified rare cells expressing NKX3.1 in benign human prostate tissue, revealing the existence of human CARNs. Finally, our lineage-tracing of basal cells indicates that these cells are also a cell of origin for prostate cancer in vivo. Based on these preliminary findings, we will pursue three linked specific aims, using a combination of genetic lineage-tracing and transplantation approaches: (1) Analysis of cell types of origin in vivo to determine whether specific cell epithelial cell types can serve as a cell of origin, and to assess whether different cells of origin may give rise to distinct tumor subtypes. (2) Analysis of tumor-initiation capability from tumors arising from distinct cell origins to determine tumor-initiating cells (TICs) can be identified and whether their frequency differs depending on the cell type of origin. (3) Molecular analysis of CARNs In mouse and human prostate tissue to identify specific markers of transformed CARNs in mice, followed by functional analyses of candidate regulatory genes, and by the identification of human CARN and transformed CARN populations from benign and tumor tissue, in conjunction with Core A. Our proposed studies will be highly synergistic with the analyses of Nkx3.1 regulation of prostate epithelial differentiation and senescence in Project 2, and of the response to DNA damage in prostate epithelial stem cells in Project 3.